The present invention relates to a gas turbine engine, and more particularly to a turbofan engine having a variable geometry fan exit guide vane (FEGV) system to change a fan bypass flow path area thereof.
Conventional gas turbine engines generally include a fan section and a core section with the fan section having a larger diameter than that of the core section. The fan section and the core section are disposed about a longitudinal axis and are enclosed within an engine nacelle assembly. Combustion gases are discharged from the core section through a core exhaust nozzle while an annular fan bypass flow, disposed radially outward of the primary core exhaust path, is discharged along a fan bypass flow path and through an annular fan exhaust nozzle. A majority of thrust is produced by the bypass flow while the remainder is provided from the combustion gases.
The fan bypass flow path is a compromise suitable for take-off and landing conditions as well as for cruise conditions. A minimum area along the fan bypass flow path determines the maximum mass flow of air. During engine-out conditions, insufficient flow area along the bypass flow path may result in significant flow spillage and associated drag. The fan nacelle diameter is typically sized to minimize drag during these engine-out conditions which results in a fan nacelle diameter that is larger than necessary at normal cruise conditions with less than optimal drag during portions of an aircraft mission.